1. Field of the Invention
The present invention relates to a reflection type lighting apparatus, and more precisely, it relates to a reflection type lighting apparatus which can be advantageously used to make a non-circular illumination area.
This application is related to the commonly assigned application U.S. Ser. No. 694,335, the disclosure of which is expressly incorporated by reference herein.
2. Description of Related Art
The present application proposes a lighting apparatus which includes a main mirror and an auxiliary mirror which. Examples of which are disclosed in Japanese Patent Application Nos. 2-116379, 2-116380 and 2-236418 (and corresponding U.S. Ser. No. 694,335 filed on May 1, 1991). The proposed lighting apparatuses are featured by an auxiliary mirror which reflects the light from the light source toward the main mirror.
However, in the proposed lighting apparatuses, the main mirror and the auxiliary mirror are both circular in front elevation view, and accordingly, the illumination area is also circular. On the other hand, a transmission type liquid crystal projector having a rectangular picture plane requires a non-circular illumination area. In this projector, it is preferable that the emission opening of the auxiliary mirror have a shape corresponding to the shape of the illumination area (rectangular picture plane) to illuminate a non-circular area. However, the shape of the illumination area defined by the shape of the emission opening of the auxiliary mirror results in an increase in the amount of light that is lost. Namely, a portion of the light which is emitted from the light source and reflected by the main mirror is intercepted, and accordingly, the amount of light to be reflected by the main mirror and the auxiliary mirror is decreased, resulting in an inefficient utilization of light. In the transmission type liquid crystal projector, the utilization efficiency is usually less than 10% due to reflection and absorption of light. Consequently, if there is a loss at the light source portion, as mentioned above, the utilization efficiency is further reduced, which is not practicable.